Most years, they do try to complete filming before or start filming after the night of the finale. They enjoy coming to TARcon as much as the fans enjoy having them. But there have been years that Phil and Elise haven't made it (Bertram has shown up, but not as often as both Phil and Elise.)

When it starts likely has little to do with that tweet. I don't know that there's been enough information to vet that tweet as reliable. Toronto, like Vancouver has a history of false leads just prior to the start of filming, for various reasons, and the best thing to do if you come across raw tweets or FB mentions like this is to relay it Peach or one of the detectives. There are ways to test these things, and in the interest of avoiding dead ends and false leads, it's best to let the detectives know and let them make the judgments.